160 
Biology of Pediculus humanus 
act of moulting sooner than the females, I have failed to observe such 
a difference in over 100 capitis and many corporis raised to maturity, 
their ages being accurately recorded. 
Loss of Life during Development. 
When raised experimentally, a certain proportion of lice always 
die in the course of their development from the egg to the adult stage. 
Apart from accidents, in my experience, death may follow (a) arrested 
development in the egg, ( b) failure of the larva to issue properly from 
the egg, (c) failure to cast off the old skin when moulting (a rare occur¬ 
rence), (d) inability to feed from weakness probably due largely to 
starvation, (e) overfeeding. A common cause of death due to ( a-d) is 
a too hot and dry atmosphere, coupled, in the active stages, with 
infrequent opportunities of feeding. Deaths from overfeeding are the 
result of too long intervals elapsing between meals; the insects may 
literally rupture themselves. 
Corporis is less susceptible to artificial conditions than capitis. A 
large proportion of the former may be raised to maturity in the ther¬ 
mostat at 30° C. even when they are fed but twice a day: thus, under 
these relatively unfavourable conditions, starting with the 1st stage 
larva, Hindle (ms.) raised 59-3 % (944 out of 1590) of them to maturity, 
and Harrison (ms.) raised 12 out of 14. 
Under the same conditions, I have repeatedly failed with capitis ; 
they died in large numbers from the causes above enumerated (a-d). 
Starting with innumerable fertile eggs, many shrivelled up and hundreds 
of larvae died in the act of hatching, and in the end only a few adults 
were obtained. 
The degree of success obtained in raising lice, depends entirely upon 
whether the conditions are suitable or not.. With adequate precautions, 
practically 100 % of either corporis or capitis can be successfully reared 
upon man, where the insects find a suitable temperature, and most 
important, unlimited opportunities of feeding. In short, to obtain the 
best results, it is necessary as far as possible to imitate the natural 
conditions under which the insects live as parasites. By the methods 
described on pp. 105-109, wherein the lice were kept continuously upon 
the body, either in a felt cell or more conveniently in a wristlet, the results 
obtained are almost constant, loss of life being reduced to a minimum. 
Capitis affords the better test of the efficiency of the wristlet method. 
Thus, at the first trial, 100 were readily reared to maturity from 102 
